Bottle preforms are molded in large quantities and minimizing the molding cycle time is critical to commercial viability of the system. Formed bottle preforms must be adequately cooled down to a sufficient temperature to allow their release from the mold without surface damage or physical distortion due to warping, or to avoid crystallization of the cooling melt of plastic. The rate of cooling the bottle preform is a major factor in determining overall cycle time.
In the field of injection molding, cooling a formed bottle preform located on a core is very well known and commonly used in industry.
For example, U.S. Pat. No. 5,571,470 entitled "Method for Fabricating a Thin Inner Barrier Layer within a Preform" issued to the Coca-Cola company on Nov. 5, 1996 and discloses a conventional apparatus for cooling formed bottle preforms. An elongate core rod is shown having an lengthwise inner channel. Cooling fluid circulates in the lengthwise inner channel for cooling the formed preform.
U.S. Pat. No. 5,582,788 entitled "Method of Cooling Multilayer Preforms" issued to Contentional PET Technologies Inc. on Dec. 10, 1996 and discloses a conventional apparatus for cooling formed bottle preforms. A cylindrical core is shown inserted within a mold cavity, including a formed bottle preform. The cylindrical core includes a lengthwise bore to receive circulating water within the interior of the core to cool the formed bottle preform during operation.
The book entitled "Mold Engineering" published by Hanser/Gardner publications, written by Herbert Rees, copyright 1995, describes bubbler mold cooling and baffle assist mold cooling on page 298.
An elongated core having a lengthwise bore is cooled through a bubbler and a conventional cooling medium. The bubbler is essentially a hollow tube having one end extending lengthwise into the lengthwise bore of the elongated core. The other end of the bubbler is connected to a inlet manifold port for supplying the cooling medium. The lengthwise bore forms a mouth at the open end of the core and is connected to a exit manifold port permitting water to exit the core.
Water enters the inlet manifold port, travelling through the bubbler into the elongated core and out of the open end of the elongated core into the exit manifold port. Water leaves the open end of the bubbler and contacts an inner surface of the core at a substantially perpendicular angle to the flow of cooling fluid from the bubbler.
Baffle assist mold cooling improves cooling by redirecting the flow of water along a differing path for more uniform cooling along the length of the elongated core. The example illustrates a helical path formed on the outer surface of the bubbler for directing the flow of water.
U.S. Pat. No. 4,208,177 entitled "Fluid Cooling of Injection Molded Plastic Articles" issued to Logic Devices on Jun. 17, 1980 and discloses an apparatus for cooling an injection molded plastic article. A pair of dies are illustrated, one having a mold cavity, the other having a core. The core includes a hollow chamber, inlet pipe and outlet pipe. The inlet pipe extends lengthwise into the hollow chamber towards an end plug. An outlet pipe is connected at a distant end of a side wall of the chamber. Cooling liquid circulates from the inlet pipe into the chamber and exits the outlet pipe. The cooling liquid streams from the inlet pipe and contacts a surface of the chamber at a substantially perpendicular angle to the flow of cooling fluid.
U.S. Pat. No. 5,631,030 entitled "Cooled Injection Core for an Integrated Injection Blow Mold machine" issued to Electraform Incorporated on May 20, 1997 and discloses an apparatus for creating a spiral flow path between the water inlet and the water outlet of a core. The cooling liquid leaves the inlet pipe located within a bore of a core and contacts an inner surface of the bore at a substantially perpendicular angle to the flow of cooling fluid.
U.S. Pat. No. 4,966,544 entitled "Injection Mold Having Cooling Fins" issued to Fuji Photo Film Company on Oct. 30, 1990 and discloses a series of baffles to direct the flow of coolant in a core. A core and cavity are illustrated within the disclosure. The core includes a supply port, an elongate hollow bore, and a discharge port. An elongate baffle plate is disposed lengthwise from one end of the hollow bore in close proximity of an upper end of the hollow bore. The elongate baffle separates the supply port from the discharge port and defines a flow path in the hollow bore extending between the supply and discharge ports. A pair of heat exchange ribs extend from the side walls of the hollow bore of the core in the direction of coolant flow. The coolant enters through the supply port, flows down one side of the hollow bore defined by the baffle plate, flows around the heat exchange ribs, down the other side defined by the baffle plate and the hollow bore, and out the discharge port.
Product literature posted on the internet web site for Choice Mold Components Incorporated on Jul. 12, 1999 illustrates a "Turbo Water Baffle" product for use in a core. The device provides a spiral design or helix to direct and rotate the flow of coolant in a bore of a core. The cooling liquid leaves an inlet pipe and contacts a surface of a bore formed in the core at a substantially perpendicular angle to the flow of cooling fluid before flowing to an exit port.
The aforedescribed prior art devices are prone to several problems.
It is known in the prior art that a core may be cooled by circulating a coolant such as water through a central bore formed in the core. However, heat removal across the elongate core is not uniform. For example, as a melt of hot plastic travels through the mold gate, it shears, which results in additional heat. During a packing cycle, the gate region is the last area having a melt injected. As such, the hottest area of the core is the semispherical end nearest the mold gate. Crystallization may occur near the mold gate as a result of slow cooling in the crystallization temperature range affecting the quality of the molded part. Conventional prior art approaches to circulating a coolant do not address the high heat gate area of the core which result in relatively long cycle times.
It is also known in the prior art that baffles may be applied for re-directing the flow of cooling fluid along a different path to produce a more uniform cooling over the elongate body. Again, the prior art baffles do not teach or provide a solution that addresses cooling the high heat area of the core near the gate.
The prior art baffle devices add additional cost and complexities to the core, and require a relatively long cooling cycle time.
It is also known in the prior art that an inlet pipe may be centrally located within the bore of the core to deliver the cooling fluid into the bore. The stream of fluid contains a stagnation area at the high heat area of the core where the fluid cannot move and effectively remove heat from the core. This results in slower cooling and a relatively long cycle time.
It is also known that if the heat transfer characteristics could be improved by a core cooling device, then the bottle preform molding cycle time could be reduced leading to increased production.
Therefore, it is desirable to provide an invention which overcomes the aforedescribed problems of the prior art.